There are four subspecies of Pinus contorta, and one of them is sometimes considered to have two varieties. The subspecies are sometimes treated at the rank of variety.
Depending on subspecies, Pinus contorta grows as an evergreen shrub or tree. The shrub form is krummholz and is approximately high. The thin and narrow-crowned tree is high and can achieve up to in diameter at chest height. The murrayana subspecies is the tallest. The crown is rounded and the top of the tree is flattened. In dense forests, the tree has a slim, conical crown. The formation of twin trees is common in some populations in British Columbia. The elastic branches stand upright or overhang and are difficult to break. The branches are covered with short shoots that are easy to remove. The species name is contorta because of the twisted, bent pines found at coastal areas and the tree's twisted needles. Pinus contorta is occasionally known under several English names: black pine, scrub pine, and coast pine. P. contorta subsp. latifolia will hybridise with the closely related jack pine.
Needles and buds
The egg-shaped growth buds are reddish-brown and between long. They are short pointed, slightly rotated, and very resinous. Spring growth starts in beginning of April and the annual growth is completed by early July. The dark and mostly shiny needles are pointed and long and wide. The needle edge is weak to clearly serrated. The needles are in pairs on short shoots and rotated about the shoots' longitudinal axes. In Alberta above, 1 to 5 needles occur per short shoot. A population with a high proportion of three-needled short shoots occurs in the Yukon. Needles live an average of four to six years, with a maximum of 13 years.
Cones
The cones are long. The cones have prickles on the scales. Many populations of the Rocky Mountain subspecies, P. contorta subsp. latifolia, have serotinous cones. This means that the cones are closed and must be exposed to high temperatures, such as from forest fires, in order to open and release their seeds. The variation in their serotiny has been correlated with wildfires and mountain pine beetle attacks. The cones of the coastal Pacific subspecies, P. contorta subsp. contorta, are typically non-serotinous, and those of the inland Pacific subspecies, P. contorta subsp. murrayana, are completely non-serotinous.
Ecology
Pinus contorta is a fire-dependent species, requiring wildfires to maintain healthy populations of diverse ages. The bark of the lodgepole pine is fairly thin, minimizing the tree's defense to fire; however, the heat of fire opens the cones to release the seeds. This allows the species to regenerate and maintain its place in the forest habitat. One plant community in which Pinus contorta is found is the closed-cone pine forest of coastal California. Excessive wildfire prevention disrupts the fire ecology. The stands are usually so densely populated that the trees self-thin, or out-compete each other, leaving dead trees standing. These become a dry ladder fuel that can accelerate the fire to the crown of living trees. When the fire reaches the crowns of the trees, it can jump from tree to tree and becomes relatively unstoppable. The natural fire regime for this species is primarily driven by climate. The fires occur most often after years of drought. Pinus contorta occurs from the upper montane to the subalpine region. These types of forests experience a lot of moisture in the form of snow in the winter due to their altitude. The density of the tree stand also inhibits the establishment of an understory. With all of that being said, the likelihood of a surface fire occurring is rare. Thus, infrequent but severe fires dominate this species. An example of the climate that plays a huge role in the fire regime of Pinus contorta is quite complex. There are three different oscillations that play a major role in droughts. These are the Pacific Decadal Oscillation, Atlantic Multi-decadal Oscillation and El Nino. A combination of these oscillations being in effect or not in effect have a global effect on the water available to these forests. So when the AMO +, ENSO – and PDO –, there is going to be a drought and likely a severe subalpine fire. Suillus tomentosus, a fungus, produces specialized structures called tuberculate ectomycorrhizae with the roots of lodgepole pine. These structures have been shown to be the location of concentrations of nitrogen-fixing bacteria which contribute a significant amount of nitrogen to tree growth and allow the pines to colonize nutrient-poor sites.
Threats
This species is attacked by blue stain fungus, distributed by the mountain pine beetle from its mouth. A study released in 2011 concluded that Pinus contorta could experience significant reductions in distribution due to climate change by the late 21st century.
Uses
Construction
of Pinus contorta have been planted extensively in Norway, Sweden and UK for forestry, such as timber uses. It is also commonly used for pressure treated lumber throughout North America.
